Health effects of microplastics

Given the rise of plastic contamination worldwide, the health effects of microplastics on humans is a growing concern.

As seen in the previous article What are microplastics and nanoplastics?, microplastics (MPs) and (NPs) are tiny plastic particles that can enter the body via foods such as water, sugar, salt, fish, seafood and produce. The good news is that, in theory, we should be able to excrete up to 90% of the ingested particles (1).

The extent at which MPs get absorbed into our bodies, organs and cells depends on the size of the particles. The numbers below are estimates:

• < 150 micrometres in diameter (~0.3% of ingested particles): pass through the digestive system, enter the lymphatic and circulatory systems
• ≤ 20 micrometres in diameter: get into organs
• 0.1-10 micrometres in diameter (~0.1% of ingested particles): cross the blood-brain barrier, placenta and cell membranes (1, 2)

In addition, MPs also make their way into our bodies via inhalation (i.e. breathing). In fact, it is estimated that can take in more particles from dust than from eating foods contaminated with MPs (2).

Health effects of microplastics

There is not a lot of information available about the health effects of MPs in humans. Many of the suspected risks have been extrapolated from animal and in vitro (i.e. experiments on cells) studies. Evidence on humans come from studies on workers exposed to chemical toxins or individuals with plastic implants that degrade with time. It is estimated that most people are exposed to lower levels of MPs and NPs than those populations (3).

The potential detrimental health effects of MPs and NPs include, but are not limited to:

• Oxidative stress (2), which can lead to several health issues
• Toxicity to the immune system, leading to excessive suppression or activation of the immune system and abnormal inflammatory responses (2)
• In the case of MPs and NPs that enter the body via inhalation, toxic effects on lung cells and macrophages, as well as respiratory issues such as asthma-like bronchial reactions, chronic pneumonia, chronic bronchitis and pneumothorax (1)

Health effects of additives

Many of the detrimental health effects of microplastics are due to the chemical substances that are found associated to them (1), including:

• Bisphenol A (BPA): used in polycarbonate plastics and the internal coating of food cans and jar/bottle lids. BPA has been identified as a hormone disruptor (1, 2, 4) and linked to obesity, cardiovascular disease, reproductive issues and breast cancer (1).
• Phthalates: used as plasticizers to improve physical characteristics of plastic items. They have been identified as endocrine disruptors (1, 4) and potential carcinogenic agents (1).
• Heavy metals: these are elements with a high atomic mass and higher density than water, which are naturally present in the environment. They are used in plastics manufacturing with various purposes (1). In addition, MPs can accumulate heavy metals present in the environment (e.g. in the ocean) over time (4). Large concentrations of heavy metals can cause cellular damage. Some heavy metals can bind to oestrogen receptors and may lead to breast cancer. Some can cause DNA damage, increase oxidative stress, negatively affect the central nervous system and kidneys (1).
• Flame retardants: flame retardants are used in electrical/electronic products, building materials, textiles and transport. They may be used as additives in products made of plastic or adhere to the surface of ready-made plastics. Detrimental health effects of flame retardants include reproductive and immune system toxicity, and interference with thyroid hormones, depending on the specific type (1). Flame retardants have been found in human milk and residue from water purification plants (1), suggesting they can enter the human body through drinking water.

Some studies have suggested that MPs found in combination with other hazardous chemicals may have a higher toxic load than either found alone (4).

References

1. Campanale C, Massarelli C, Savino I, Locaputo V, Uricchio VF. A Detailed Review Study on Potential Effects of Microplastics and Additives of Concern on Human Health. Int J Environ Res Public Health. 2020 Feb;17(4).
2. Barboza LGA, Dick Vethaak A, Lavorante BRBO, Lundebye A-K, Guilhermino L. Marine microplastic debris: An emerging issue for food security, food safety and human health. Mar Pollut Bull. 2018 Aug;133:336–48.
3. Zarus GM, Muianga C, Hunter CM, Pappas RS. A review of data for quantifying human exposures to micro and nanoplastics and potential health risks. Sci Total Environ. 2021 Feb;756:144010.
4. Jiang B, Kauffman AE, Li L, McFee W, Cai B, Weinstein J, et al. Health impacts of environmental contamination of micro- and nanoplastics: a review. Environ Health Prev Med. 2020 Jul;25(1):29.

[Photo by Marc Newberry on Unsplash]

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